Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1244 PM EDT Wed Oct 23 2019 Valid Oct 23/1200 UTC thru Oct 27/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Prelim Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Central U.S. cyclone through early Thursday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Above average A positively tilted trough digging south from the Upper Mid-west into the central Rockies is in good agreement among the models. In response, mid-level impulses rounding the trough with interact with surface features that will continue to produce precipitation from the northern Rockies across the northern Plains. Meanwhile, an associated cold front will continue to trek northeast off of Maine. As a shortwave dives south from the central Rockies overnight into the southern Plains, cyclogenesis will develop. It was at this point where models struggled to determine the evolution of this piece of energy with the GFS too fast. However, the latest 12Z GFS is coming into better agreement, thus feel a general model blend across the CONUS will suffice. Stronger shortwave dropping through Rockies; closing off across the southern Plains through Saturday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF, ECENS mean, UKMET, GEFS (lesser weight) Blend Confidence: Slightly Below average The aforementioned shortwave will calve off the main trough, splitting from the northern stream. Now all models are illustrating a closed mid-level low dropping south into the southern Plains. Though the differences among the models continue with position, timing and intensity. The 12Z GFS trended slower and is coming more in line with the model diagnostic preferences over the past several days: EC/EC mean/UKMET. The 00Z CMC continues to be the slowest solution, along with the latest SREF mean; thus will not use within the blend. A lot depends on the shortwave interaction with both the departing trough axis moving east Friday and also the approaching trough in the west. The previous runs of the GFS had the shortwave being carried by the departing trough, while the non-NCEP members had the approaching trough carry the existing shortwave/closed low northeast. It would seem that a slower solution with respect to the closed low is most fitting given the anomalously high heights into Alaska (ridging by late in the period) and the cooler temperature diving into the Rockies. In addition, the strengthening jet axis to the north also favors a slower progression. So with the GFS coming into better agreement with the EC/EC mean/UKMET, could feasibly incorporate this model into the blend. However, for now, since the GFS is still too fast, will use the GEFS mean. Again, the position and timing of the shortwave and how it interacts with the approaching trough will ultimately determine the track/intensity of the surface low. Shortwave troughing across Pacific Northwest Friday-Saturday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Average The anomalous ridge over the eastern Pacific and western U.S. mid to late week will be shunted and broken down some as another strong shortwave trough approaches from the Gulf of Alaska. While the previous model runs showed a bit better agreement among the GFS/EC with this feature, the EC/ECmean and now the the 12Z GFS is showing a sharpening of the trough as it moves through the northern Rockies. This differs from the rest of the model guidance. Regardless of this variability, the QPF differences are negligible. Thus with a general model blend, this should take care of any subtle difference that exist within the mass fields this late in the forecast period. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Pagano